1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus wherein ultrasonic images such as an M-mode display image (motion image), a B-mode display image (tomographic image), a D-mode (a PWD-mode, a CWD-mode) display image (bloodstream velocity image) or a DF-mode (a BDF-mode, a MDF-mode) display image (CFM image: Color Flow Mapping Image) are obtained by causing ultrasonic beams to scan a living body for the purpose of diagnosis.
2. Description of the Related Art
This type of ultrasonic diagnostic apparatus is used for the diagnosis of a circulatory system, for example, a heart. In this case, a doctor obtains a B-mode display image as anatomical data of the heart, obtains an M-mode display image as functional data of the heart, or obtains a D-mode (a PWD-mode, a CWD-mode) display image or a DF-mode (a BDF-mode, a MDF-mode) display image as data of bloodstream in the heart.
In general, the B-mode display image and the D-mode display image are simultaneously obtained and observed for effective diagnosis of the heart. The D-mode display image is obtained by using the Doppler effect. In this case, a moving object is in general a flow of blood cells. Thus, in order to cause the Doppler effect, it is necessary that the direction of the bloodstream is not at right angles with the ultrasonic beams.
Since the blood cells flow along the surface of the living body, a linear scan wherein ultrasonic beams are transmitted/received in a direction perpendicular to the surface of the body is not suitable. Rather, a sector scan wherein ultrasonic beams are transmitted/received in a direction non-perpendicular to the surface of the body is suitable.
However, the B-mode image obtained by the sector scan has a sectional shape, and a visual field near a probe is very narrow. Thus, this B-mode image is observed with some difficulty, compared to a rectangular image such as a B-mode obtained by a linear scan or a trapezoidal image obtained by a trapezoidal scan.